JustDecompile version 2011.2.1017.4
It seems that enums nested in a generic type decompile to invalid C# code (VB as well). For example, decompiling System.Collections.Concurrent.BlockingCollection<T>, you will find a nested enum called OperationMode, which the current version of JustDecompile decompiles to
private enum OperationMode<T>
The <T> should not be part of the name, even though in the IL it is part of the name.
Btw. looking at the IL for enums, I also noticed that the enum is missing the declaration for value__, and also the explicit value assigned to the members are not shown. It might be worth showing the the members as the complete IL definition?
.field public static literal valuetype System.Collections.Concurrent.BlockingCollection`1/OperationMode<!T> Add = int32(0)